N-Acyl proline

Triacycloxyborohydrides (62), derived from NaBH (1 equiv.) and (S)-N-acyl-proline (3 equiv.), were found to reduce 3,4-dihydropapaverine (89) in tetrahydro-furan to (S)-norlaudanosine (90) hydrochloride in 60% optical yield93. In some cases (90) was obtained in even higher optical purity (e.e. = 70-86 %). 

Partial hydrolysis of stendomycin by concentrated hydrochloric acid at room temperature yielded a mixture of peptides which were separated by ion-exchange chromatography. The isolation of N-acyl proline and N-acyl Pro-N-MeThr identified the N-terminal end of the peptide chain. Partial hydrolysis or methanolysis of dihydrostendomycin preferentially cleaved the peptide chain after the a-aminobutyric acid residue, allowing the isolation of two peptides containing the six or seven first amino acids from the N-terminal end. 

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